The study looked at how different amounts of nitrogen fertilizer and a special bio-fertilizer affected rice yields in Iran. They found that increasing nitrogen fertilizer up to 75 kg/ha increased grain and biological yields, but more didn't help. The bio-fertilizer increased grain yield overall. More nitrogen increased grain quality, but the bio-fertilizer didn't affect this. Overall, adding more nitrogen increased rice yields, while the bio-fertilizer only helped with grain yield.